Fission product getter

ABSTRACT

A getter element includes a getter material reactive with a fission product contained within a stream of liquid and/or gas exiting a fuel assembly of a nuclear reactor. At least one transmission pathway passes through the getter element that is sufficiently sized to maintain a flow of the input stream through the getter element at above a selected flow level. At least one transmission pathway includes a reaction surface area sufficient to uptake a pre-identified quantity of the fission product.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional of and claims priority to U.S.patent application Ser. No. 15/451,719, filed Mar. 7, 2017, which claimspriority to U.S. Provisional Patent Application No. 62/305,272, filedMar. 8, 2016, both of which are herein incorporated by reference intheir entirety.

TECHNICAL FIELD

The present disclosure generally relates to a fission product getterdevice and a method of fabricating a fission product getter device.

SUMMARY

A fission product getter apparatus is disclosed, in accordance with oneor more illustrative embodiments of the present disclosure. In oneillustrative embodiment, the fission product getter apparatus includes agetter body including a volume of getter material and having a voidstructure. In another illustrative embodiment, the getter material isreactive with a nuclear fission product contained within a fluid flowfrom a nuclear fission reactor. In another illustrative embodiment, thegetter body has a determined volume parameter sufficient to maintainflow of the fluid through the void structure of the getter body for aselected period of time. In another illustrative embodiment, thedetermined volume parameter of the getter body has the determined volumeparameter and provides a void volume within the getter body sufficientto maintain expansion of the getter body below a selected expansionthreshold over a selected period of time.

The foregoing is a summary and thus may contain simplifications,generalizations, inclusions, and/or omissions of detail; consequently,those skilled in the art will appreciate that the summary isillustrative only and is not intended to be in any way limiting. Otheraspects, features, and advantages of the devices and/or processes and/orother subject matter described herein will become apparent in theteachings set forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example nuclear fission reactor with a fastnuclear reactor core.

FIG. 2 illustrates an example getter body formed by a volume includinggetter material.

FIG. 3A illustrates an example getter element including a getter bodysupported by capping elements.

FIG. 3B illustrates another view of one of the capping elementsillustrated in FIG. 3A.

FIG. 4A illustrates another example getter element including a getterbody supported by capping elements.

FIG. 4B illustrates another view of one of the capping elementsillustrated in FIG. 4A.

FIG. 5A illustrates an example support structure suitable for use in agetter element.

FIG. 5B illustrates a simplified schematic view of another examplesupport structure suitable for use in a getter element.

FIG. 6 illustrates another example support structure suitable for use ina getter element.

FIG. 7 illustrates an end-on view of another example getter body.

FIG. 8 illustrates an end-on view of yet another example getter body.

FIG. 9 illustrates a cross-sectional view of a fuel pin of a nuclearreactor equipped with an example getter element.

FIG. 10 illustrates a cross-sectional view of a fuel pin of a nuclearreactor equipped with two example getter elements arranged in seriesbetween nuclear fuel and a fission plenum.

FIG. 11 illustrates a top view of an example fuel assembly including aset of fuel pins containing getter elements.

FIG. 12 illustrates a perspective view of a nuclear reactor coreincluding a set of fuel assemblies.

FIG. 13 illustrates example operations for forming a getter body for usein cleaning a fission gas output stream of a nuclear reactor.

FIG. 14 illustrates a series of example operations for preparing agetter process mixture and forming a getter body with a plurality ofvoids.

FIG. 15A illustrates an example volume of sacrificial void-formingstructures that are spherical in shape.

FIG. 15B illustrates an example volume of sacrificial void-formingstructures that are ellipsoidal in shape.

FIG. 15C illustrates an example volume of oblate-spheroid-shapedsacrificial void-forming structures.

FIG. 15D illustrates an example volume of prolate-spheroid-shapedsacrificial void-forming structures.

FIG. 16 illustrates a conceptual view of a portion of a consolidatedvolume of a getter process mixture.

FIG. 17 illustrates graph depicting the percentage of theoreticaldensity (TD) of a getter process mixture achieved as a function ofapplied die pressure.

FIG. 18A illustrates an example getter body including sacrificialvoid-forming structures and a getter material.

FIG. 18B illustrates the example getter body of FIG. 19A afterundergoing thermal or chemical treatment that decomposes the sacrificialvoid-forming structures, leaving behind voids.

FIG. 19A illustrates a radial cross-section of the fabricated getterelement and depicts a number of pores that form the overall voidstructure of the getter element.

FIG. 19B illustrates a zoomed-in view of a single pore of the fabricatedgetter element of FIG. 20A.

FIG. 20 illustrates a series of example additive fabrication operationsfor forming a getter element.

FIG. 21 illustrates an example getter body formed via an additivefabrication process.

FIG. 22 illustrates another example getter body formed via an additivefabrication process.

FIG. 23 illustrates yet another example getter body formed via anadditive fabrication process.

FIG. 24 illustrates example operations for forming a getter element viaa sacrificial templating process.

FIG. 25 illustrates example operations for forming a getter element viaa direct foaming operation.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented here.

The present disclosure is directed to various embodiments of a getterelement for removing one or more fission products from a gas and/orliquid flow, such as fission products formed during a reaction processwithin a nuclear fuel of a nuclear reactor. The getter element includesone or more internal passages that facilitate a continuous throughput ofthe fluid (liquid and/or gas) flow, and also includes getter materialthat chemically reacts with a target fission product to remove thefission product from the flow. The disclosed technology is suitable forimplementation in a variety of nuclear reactors including withoutlimitation fast nuclear reactors, breeder reactors, breed and burnreactors, and/or in some cases traveling wave reactors. The presentdisclosure is further directed to various methods of forming the getterelement.

FIG. 1 illustrates an example nuclear fission reactor 130 with a fastnuclear reactor core 132. The fast nuclear reactor core 132 is disposedin a reactor vessel 140 surrounded by a guard vessel 136. In oneimplementation, the fast nuclear reactor core 132 includes a nuclearfission igniter (not shown) that provides neutrons for the fissionreaction of fissile nuclear fuel. The nuclear fission reactor 130includes a number of fuel assemblies (e.g., a fuel assembly 138 in ViewB), and each fuel assembly further includes multiple fuel elements,which are also referred to herein as fuel pins. In one implementation ofthe disclosed technology, the individual fuel pins each further includea mechanism for collecting one or more fission products from an inputstream, as described below with reference to Views B, C, and D.

The fast nuclear reactor core 132 typically contains a coolant, such asa pool of coolant (such as liquid sodium) or loops through which coolantmay flow throughout the nuclear fission reactor 139. In some reactors,there exists a reservoir of coolant in headspace 148 above the fastnuclear reactor core 132. Heat exchangers (not shown) may rest near orin contact with the reservoir of coolant to aid in transporting heataway from the fast nuclear reactor core 132.

Referring to View A, the nuclear fission reactor 130 includes a numberof fuel assemblies shown in greater detail in View B (e.g., the fuelassembly 138). Each fuel assembly further includes multiple fuel pins,such as a fuel pin 120 (shown in View C). View B illustrates an array142 of nuclear fuel assembly devices suitable for use within the fastnuclear reactor core 132. Each assembly includes multiple fuel pins(e.g., a fuel pin 120). Although other device shapes and arrayconfigurations are contemplated, the example nuclear fuel assemblydevices of FIG. 1 each include a solid hexagonal tube surrounding.Non-hexagonal tubes may also be used on some implementations. Componentsof an individual fuel assembly device 138 within the array 142 are shownin further detail in Views C and D.

As shown in View C, the nuclear fuel assembly device 138 surrounds aplurality of elongated fuel elements, such as the fuel pin 120. Whennuclear fission occurs within a fuel pin, fission products are createdthat can contribute to a building pressure within the pin. In somereactors, fuel pins are designed to include a large plenum area toaccommodate this pressure at high burn-ups. Other reactors may includefuel pins designed to vent gases to relieve pressure, such as venting toallow the fission products to flow into contact with a coolant reservoirin the headspace 148. Since some fission products may be volatile, thisventing can pose a risk.

Both venting and non-venting fuel pin designs can benefit from theherein-disclosed technology, which generally provides tools andtechniques for removing of one or more fission products from a fluidflow within the nuclear fission reactor 130.

Components of the fuel pin 120 are shown in greater detail in View D,described below. In one implementation, the tubular structure of each ofthe individual fuel assembly devices, such the nuclear fuel assemblydevice 138, allows coolant to flow past the fuel pins throughinterstitial gaps between adjacent tube walls. Each tube also allowsindividual assembly orificing, provides structural support for the fuelbundle, and transmits handling loads from a handling socket to an inletnozzle. Fuel pins typically consist of multiple nuclear fuel rods (suchas uranium, plutonium or thorium) surrounded by cladding (and sometimesan additional barrier and/or liner) to separate the radiative materialand the coolant stream. Individual pins of the nuclear fuel assemblydevices 138 in the fast nuclear reactor core 132 can contain fissilenuclear fuel and/or fertile nuclear fuel depending on the originalnuclear fuel rod material inserted into the pin and the state ofbreeding within the pin.

An example fuel pin 120 is shown in greater detail in View D. The fuelpin 120 includes fuel 122, a getter element 100, and an optional plenumarea 124. The getter element 100 stores a material (not shown) that ischemically reactive with a fission product 110 included in an inputstream 108 received from the fuel 122. For example, the input stream 110includes one or more fission products created during nuclear fission ofthe fuel 122. The getter element 100 includes at least one internalfluid flow path that facilitates continuous transmission of a gas and/orliquid through the getter element 100. The fluid flow path may be, forexample, one or more elongated channels, interconnected pores,microfluidic structures, etc. The fluid flow path through the getterelement 100 provides a surface area internal to the getter element 100that may chemically react with the fission product 110 to remove thefission product 110 from the input stream 108, and thereby create anoutput stream 112 with a lower density of the fission product 110 thanthe input stream 108. In various implementations, the fission product110 may be volatile or non-volatile. Although plenum area 124 is shownabove the getter element 100, and the getter element 100 above the fuel122, it is to be appreciated that these components may be placedrelative to each other in any suitable order and manner.

The various examples of fuel pins (e.g., the fuel pin 120) describedherein may represent venting or non-venting fuel pins. In a venting fuelpin, the plenum area 124 is, at times, in fluid communication with theheadspace 148 in a nuclear reactor, or other appropriate gas reservoir.For example, the fuel pin may include various vents or openings thatfacilitate fluid communication between the plenum 124 and the headspace148.

As used herein, the term “getter element” (as in the example getterelement 100) is meant to refer to any structure including a “gettermaterial” capable of chemically reacting with a fission product andthereby removing a quantity of the fission product from an input stream.Getter material may be incorporated within or formed into a “getterbody.” For example, a getter body may be a free-standing structure,collection of particulates (e.g., powder), small capsules or pellets.The getter body may include the getter material alone or the gettermaterial in addition to one or more other non-getter materials that donot react with the fission product 110. In some cases, the getterelement includes a getter body and also includes a container for holdingthe getter body.

The getter element 100 includes one or more channels for placing theinput stream 108 in fluid communication with a getter body. In oneimplementation, the getter body has characteristics designed to maximizesurface area of contact between a getter body and the input stream 108passing through the getter element 100. For example, the getter body mayinclude pores or other channels that increase its total surface area. Inadditional and/or alternative implementations, the getter element 100includes a container with one more diffusing elements for directing theinput stream 108 into contact with the getter body. Fluid space withinor throughout, the getter element 100 and the getter body allows theinput stream 108 to contact the getter material and chemically react toremove the fission product 110 from the input stream.

In some implementations, the getter element 100 is not included in afuel pin (e.g., the fuel pin 120), as shown. Rather, the getter element100 is positioned elsewhere within the nuclear fission reactor 130 at aposition that is accessible to targeted fission products. For example,the getter element 100 may be positioned above the reactor core withinthe reactor vessel and/or in headspace 148 of the nuclear fissionreactor 130 to receive and react with fission product(s) fluid exitingthe fuel subassemblies.

Notably, certain structures of the example nuclear fission reactor 130have been omitted from FIG. 1, such as coolant circulation loops,coolant pumps, heat exchangers, reactor coolant system, etc., in orderto simplify the drawing. Accordingly, it should be understood that theexample nuclear fission reactor 130 may include additional structuresnot shown in FIG. 1.

FIG. 2 illustrates an example getter body 200 formed by a volumeincluding getter material 204. The getter body 200 includes at least onethrough-channel (e.g., a through-channel 220) for transmitting a flow ofan input stream 208 through the getter body 200. The through-channel(s)may extend along a longitudinal length of the getter body 200 (e.g., inthe direction of the input stream 208, as shown) and/or may extend inone or more other directions so as to facilitate transport of gas fromone side of the getter body 200 to another opposite side.

The through-channel(s) of the getter body 200 assume a variety ofdifferent forms in the various implementations disclosed herein.Suitable forms include without limitation interconnected voids or pores,engineered pathways, and/or separations between discrete particles(e.g., in implementations where the getter body is a loose powder asdescribed further with respect to FIG. 3, below).

The input stream 208 may be gaseous, liquid, or a combination thereof,and further includes a fission product 210, which may be gaseous,liquid, solid, dissolved, suspended, or a combination thereof. In oneimplementation, the getter material 204 includes one or more materialsthat are chemically reactive with the fission product 210. In thisregard, as the input stream 208 containing the fission product 210contacts the getter body 200, the getter material 204 chemically reactswith the fission product 210 to form a byproduct that is retained withinthe getter body 200 while the remainder of the input stream 208 exits ormoves past or through the getter body 200 as an output stream 212. Thus,the output stream 212 contains less fission product 210 than the inputstream 208. The process of removing the fission product 210 from theinput stream 208 via chemical reaction with a getter material is alsoreferred to herein as an “uptake” (e.g., the getter body 200 “uptakes”the fission product 210). In one implementation, the getter body isspecifically engineered to provide for uptake of substantially all of aselect fission product produced within a fuel pin over a period of time,such as over the effective lifetime of the fuel pin. As used herein,uptake of “substantially all” of a select fission product refers touptake of at least 95% and some cases more than 95% of the selectfission product.

The through-channel(s) of the getter body 200 serve multiple purposes.First, the existence of these channel(s) helps to relieve pressure inareas of the getter body 200 and/or corresponding fuel pin by allowingcertain content (e.g., inert gases) to escape. Second, the existence ofthese through-channel(s) provides areas for the getter body 200 toexpand into, such as at high burnup rates, thereby decreasing alikelihood of potential damage to associated areas of an associated fuelpin and or fuel subassembly. In one implementation, thethrough-channel(s) have a sufficient volume to maintain a through-flowabove a preselected flow level despite expansion of the getter materialwithin a predetermined range of thermal expansion.

Third, the existence of these through-channel(s) increases availablesurface area that can react with the fission product 208. In oneimplementation, the surface area of these through-channel(s) isspecifically designed to facilitate uptake of a specific calculatedquantity of the fission product 208, such as substantially all of thefission product 208 expected to be produced by an associated fuel pinover a given interval of time.

The fission product 210 of the input stream 208 may be volatile ornon-volatile fission product. Example volatile fission products includewithout limitation: cesium (Cs) or a Cs-based compound (e.g., Cs₂, CsBr,Cs₂I₂, CsI, etc.), rubidium (Rb) or a Rb-based compound (Rb, Rb₂, RbI,RbBr, etc.), strontium (Sr) or a Sr-based compound (Sr, etc.), andiodine (and it compounds). Example non-volatile fission products includewithout limitation Zirconium, Molybdenum, Neodymium, etc.

The getter material 204 includes any material known in the art aschemically reactive with the fission product 210. Although a variety ofmaterials may be suitable getter materials, some implementations of thedisclosed technology include metal oxides within the getter material,such as one or more of zirconium oxide (e.g., ZrO₂), titanium oxide(e.g., TiO₂), molybdenum oxide (e.g., MoO₂, MoO₃), niobium oxide (NbO₂,Nb₂O₅), tantalum oxide (e.g., Ta₂O₅), etc. Because the getter materialsconsidered do not show equivalent reactivity with all fission productsof concern, the getter material may also be composed of a mixture ofcomponents, with the mixture composition tailored to maximize reactionbetween the getter material and one or more targeted fission products(e.g., 75%-Ta₂O₃/25%-Nb₂O₃ mixtures). Although in some embodiments itmay be beneficial to have these disparate components intermixed, inothers it may be beneficial to have discrete layers to selectivelyremove targeted fission products from the fluid at preferential stagesto prevent potential detrimental interactions with subsequent layers ofthe getter material. The getter material may also include one or morenon-reactive components such as binders, structural stabilizers, etc.

In one implementation, the getter material 204 includes one or morematerials that react with cesium (Cs) or a Cs-based compound. In thesame or another embodiment, the getter material 204 includes at leastone material that reacts with Rubidium (Rb) or a Rb-based compound. Inthe same or another embodiment, the getter material 204 includes atleast one material that reacts with Iodine or an iodine-based compound.

In FIG. 2, the getter body 200 is shown to be a cylindrically-shapedsolid structure including a void structure 206 (e.g., pores). In oneimplementation, the void structure 206 includes randomly or regularlydistributed pores forming an open pore structure. The distributed poresmay be selectively engineered in size, shape, inter-connectivity,structural stability, distribution schema, etc. There exist a variety ofsuitable processes for forming the void structure 206 and/or otherchannels within the getter body including without limitation sacrificialtemplating, additive manufacturing, template replication, and directfoaming. These methods are discussed in greater detail below.

In one embodiment, the void structure 206 of the getter body 200 isformed via a sacrificial templating process. For example, the voidstructure 206 may be formed by mixing the getter material 204 with avoid-forming material. Voids are formed by removing (e.g., burning offor dissolving) the void-forming material. As a result of the removal ofthe void-forming material, voids (e.g., pores or cells) are formedthroughout the volume of getter material 204 of the getter body 200. Oneexample of implementation of a sacrificial templating procedure isdescribed by Andre R. Studart et al. in Processing Routes to MacroporousCeramics: Review, J. Am. Ceram. Soc. 89 [6] 1771-1789 (2006), which isincorporated herein by reference in the entirety. A variety oftreatments may be suitable for processing the void material removal fromthe getter material and form the void structure, including any one ormore of dissolving, heat treatment (e.g., during sintering or during adedicated burn-off cycle), etc. Further details of example sacrificialtemplating processes are discussed in greater detail with respect toFIGS. 14-20.

In another embodiment, the void structure 206 of the getter body 200 areformed via an additive manufacturing process. For example, the getterbody 200 may be fabricated via a three-dimensional printing process. Inthis regard, the void structure 206 of the getter body 200 may bedirectly engineered and the formation of which may be directlycontrolled via the manufacturing process. Selective laser sintering,used to three-dimensionally print materials, may be additionally oralternatively appropriate and is generally described in U.S. Pat. No.4,863,538, filed on Oct. 17, 1986, which is incorporated herein byreference in the entirety. Further details of example additivemanufacturing processes are described with respect to FIG. 20-23, below.

In another embodiment, the void structure 206 of the getter body 200 isformed via a template replication process. For example, pores may beformed through impregnation of a void structure (e.g., cellular orporous structure) with a getter material suspension (or precursorsolution), resulting in a volume of porous getter material exhibitingthe same (or nearly the same) morphology as the original porousmaterial. One example of a replica procedure is described by Andre R.Studart et al. in Processing Routes to Macroporous Ceramics: Review, J.Am. Ceram. Soc. 89 [6] 1771-1789 (2006), which is incorporated above byreference in the entirety. Basic procedural steps in templatereplication are described with respect to FIG. 24.

In another embodiment, the void structure 206 of the getter body 200 isformed via a direct foaming process. For example, the void structure 206of the getter body 200 may be formed through incorporation of a gas(e.g., air) into a suspension or liquid form of the getter material (ora precursor of the getter material), which serves to establish a foamstructure within the suspension or liquid. The material then undergoes asetting or solidifying step, which serves to lock in the void structure206 formed within the foam. One appropriate example of a direct foamingprocedure is described by Andre R. Studart et al. in Processing Routesto Macroporous Ceramics: Review, J. Am. Ceram. Soc. 89 [6] 1771-1789(2006), which is incorporated above by reference in the entirety. Basicprocedural steps in direct foaming are described with respect to FIG.25.

In yet other embodiments, the void structure 206 of the getter body 200is formed by other physical methodologies (e.g., mechanical grinding,etching laser ablation, etc.), or chemical methodologies such aschemical etching. Notably, any two or more of the above-describedtechniques (e.g., sacrificial templating, additive manufacturing,template replication, direct foaming, chemical/physical etching,grinding, ablation, etc.) may also be used in combination to create thevoid structure 206. For example, a sacrificial templating process may beinitially used to create small voids in the getter body 200 and amachining process may thereafter be used to create larger voids, such asnear a fission gas inlet of the getter body 200.

FIGS. 3A-3B illustrate simplified schematic views of an example getterelement 300 including a getter body 302 configured to rest betweenand/or attach to capping elements 314 a, 314 b at either end. Althoughother structures are also contemplated (e.g., with respect to FIGS.4-5), the getter body 302 of FIG. 3 is a free-standing, solid elementincluding a void structure 306. In operation, the capping elements 314a, 314 b serve to provide mechanical support to the getter body 302 andto further facilitate venting of an input stream 308 through the getterelement 300.

In some implementations, the main getter body 302 is not a solid freestanding structure. For example, the main getter body 302 may be inparticulate form (e.g., powder) or be a collection of elements (e.g.,solid pellets or small capsules further storing particulates). In theseimplementations, the capping elements 314 a, 314 b may be used incombination with a container or supporting shell for containing andfurther supporting the main getter body 302.

The capping elements 314 a, 314 b are made from heat-stable materialsthat resist deformation when subjected to the high temperatures andneutron fluxes of a nuclear reactor core. Ideal candidate materials mayalso be non-reactive with fission products (e.g., a fission product 310)included in the input stream 308. Example suitable materials for thecapping elements 314 a, 314 b include, for example steels, refractorymetals/alloys, or structural ceramics.

In FIGS. 3A and 3B, the one or more capping elements 314 a, 314 b areformed from a porous material. For example, the one or more cappingelements 314 a, 314 b may include a porous metal plate 313 (e.g., porousmetal disk as shown in FIG. 2B). Other porous structures, such as vents,mesh-like material, etc., are also contemplated. In one implementation,the capping elements 314 a, 314 b are solid structures that include aplurality of through-holes, such as drilled holes. The holes may be avariety of sizes and distributions depending on specific implementationdetails such as the desired flow rate, specific getter material,targeted fission product(s), etc.

FIGS. 4A and 4B illustrate simplified schematic views of another examplegetter element 400 including a getter body 402 configured to restbetween and/or attach to capping elements 414 a and 414 b. The getterbody 402 has a void structure 406 and includes a getter material 404 forreacting with a fission product 410 included within an input stream 408,thereby reducing a concentration of the fission product 410 in an outputstream 412 as compared to the input stream 408. Unlike the porousstructure of the capping elements in FIGS. 3A, 3B, the capping elements414 a, 414 b are vented metal plates 415 (e.g., vented metal disk).Suitable construction materials and other details of the cappingelements 414 a, 414 b may be the same or similar to that described abovewith respect to FIGS. 3A, 3B.

FIG. 5A illustrates a simplified schematic view of an example supportstructure 500 suitable for use in a getter element. The supportstructure 500 includes a container portion 521 attached to endcaps 514a, 514 b. In operation, the support structure 500 may provide mechanicalsupport to a getter body and facilitate venting of an input stream 508through the getter element and/or getter body. The support structure 500may support a solid, free-standing getter body (e.g., as in the maingetter body portion 402 of FIG. 4A); alternatively, the supportstructure 500 may support a getter body that is in particulate form(e.g., powder) or otherwise represented as a collection of free-standingelements (e.g., solid pellets or small capsules further storingparticulates).

The container portion 521 may be formed from any material that providesthermal and chemical and structural stability in the presence of fluidflow, neutron irradiation, and fission products of a selected nuclearreactor environment. In one embodiment, the container portion 521 isformed from steel. Other suitable container materials could includerefractory metals or alloys, as well as structural ceramics. Althoughnot shown in FIG. 5, the container portion 521 may include a pluralityof openings about its circumference to allow for fluid and/or gas toflow through the sides of the container portion 521 as well as throughvents 515 or porous openings in the endcaps 514 a, 514 b. In variousimplementations, any suitable number, size, location, and/ordistribution of vents 515 in the capping element 514 a may be used asappropriate for design and/or safety considerations.

FIG. 5B illustrates a simplified schematic view of another examplesupport structure 502 for positioning a getter body (e.g., as in thegetter body 200 of FIG. 2 or 300 of FIGS. 3A and 3B) within a fuel pin510. The support structure 502 includes porous endcaps 514 a, 514B and acentral body 516 with number of peripheral openings (e.g., an opening518) in a cylindrical sidewall 520 to allow for intake of a fluid flowinto a center of the support structure 502 and within the getter body(not shown). In one implementation, a width W1 of the support structure502 is slightly less than a width W2 of the fuel pin 510 so as to allowa fluid flow to bypass the endcap 514 a and to enter the supportstructure 502 through one or more of the openings (e.g., the openings518) in the cylindrical sidewall 520.

FIG. 6 illustrates a schematic view of a portion of another examplesupport structure 600 suitable for use in a getter element. The supportstructure 600 includes a container portion 617 and a diffuser assembly609. The diffuser assembly 609 further includes a diffuse cappingportion 614 and a diffuse channel portion 622 (e.g., an elongatedcentral channel). In operation, a getter body (not shown) is storedwithin the container portion 617. For example, the getter body maysurround or partially surround the diffuse channel portion 622. Thediffuser assembly 609 helps to bring gas or liquid of an input stream608 into fluid communication with the getter material of the getterbody. For example, the diffuse capping portion 614 and the diffusechannel portion 622 includes openings (e.g., pores, vents, etc.) thatprovide fluid flow paths into and/or through the getter body.

The diffuse channel portion 622 is shown in FIG. 6 as a singular centralchannel with a number of holes allowing gas to freely flow between areasinternal to the diffuse channel portion 622 and areas external to thediffuse channel portion 622. However, it is to be appreciated that thesupport structure 600 may include a plurality of channels in lieu of orin addition to the diffuse channel portion 622. For example, thediffuser assembly 609 may include other channels distributed throughoutother regions of the container portion 617. In some cases, the diffuserassembly 609 includes a gas transmission channel that surrounds thegetter body, such as a porous annular channel surrounding the getterbody.

Due to the uptake of a fission product 610 into the getter body, thegetter body, over time, accumulates the fission product 610.Accumulation of fission product 610 within the getter body may result inthe reduction of fission gas flow through the container portion 617and/or throughout the getter body within the container portion 617. Insome instances, where accumulation is severe, one or more porousstructures of the getter body may be become blocked. In such cases, thediffuser assembly 609 may help to maintain a flow of the input stream608 through a getter material (not shown) regardless of this blockage.In addition, the diffuser assembly 609 may serve to ensure fluid flowthrough fluid flow paths within the getter body in the event ofvolumetric expansion of the getter material of the getter body.

The diffuse capping portion 614 may take on a variety of forms, such asthat of a porous metal or ceramic plate or a vented plate with a set ofvent holes. The diffuse channel portion 622 is also porous and may be,for example, a porous metal rod or a metal rod with a set of vent holes.Some non-metal materials (e.g., ceramics) may also be suitable forforming all or various components of the diffuser assembly 609.

FIG. 7 illustrates an end-on view of a portion of another example getterbody 702 with void structures 706. In one implementation, the getterbody 702 is sized and shaped to rest within one of the correspondingsupport structures 500 or 600 of FIGS. 5 and 6, respectively. Inoperation, the illustrated end of the getter body 702 may receive aninput stream including a fission product. When the input stream contactsthe getter body 702, getter material 704 in the getter body 702chemically reacts with one or more fission products in the input stream,removing those fission product(s) from the stream.

In FIG. 7, the getter body 702 is a free-standing solid structure. Forexample, the getter body 702 may be a porous sintered metallic orceramic structure. Although other arrangements are contemplated, thevoid structures 706 of the getter body 702 are arranged such that thesize varies as a function of position within the getter body 702. Forexample, size of the void structures 706 may generally decrease as afunction of radial distance from the center of the getter body 702. Forexample, the distribution of void structures 706 may be influenced bythe size and/or weights of void-forming structures utilized duringfabrication of the getter body 702. In this regard, void-formingstructures (e.g., such as those described below with respect to FIGS.13-20) may, when mixed with the getter material 704, act to self-sortand form a distribution (e.g., gradient distribution) via a settlingand/or agitation process.

The void structures 706 of the getter body 702 may be distributedthroughout the getter body 702 in any pattern or distribution. In someimplementations, the void structures 706 include pores in greater sizenear a fission gas inlet and pores smaller in size near a fission gasoutlet.

FIG. 8 illustrates an end-on view of a portion of another example getterbody 802 that is cylindrical in shape and includes multiple concentricregions 804 a, 804 b of getter material separated from one another bytransmission pathways (e.g., an annular-shaped void 806). Theillustrated arrangement may help to maximize a surface area of contactbetween the getter material of the getter body 802 and an input stream(not shown) that is directed through the getter body 800. In oneimplementation, the concentric regions 804 a, 804 b of getter materialare solid structures, such as sintered metallic or ceramic structures.In another implementation, the getter body 802 is formed via a powderthat fills each of a number of porous concentric shells of a gettercontainer. A variety of other structures are also contemplated (some ofwhich are described with respect to the following figures).

FIG. 9 illustrates a cross-sectional view of a fuel pin 920 of a nuclearreactor equipped with an example getter element 900. The getter element900 is shown disposed within fuel pin 920 and positioned to receive aninput stream 908 (e.g., fission gas) from nuclear fuel 922 of the fuelpin 920. For example, the getter element 900 is disposed (alone or incombination with other getter elements) at a location upstream of thenuclear fuel 922 and origination point of the input stream 908, butdownstream of a fission gas plenum 924. In another implementation, thegetter element 900 is positioned within the fission gas plenum 924(e.g., with or without space of the plenum on either or both ends of thegetter element 900).

Capping elements 914 a and 914 b provide barriers between the getterelement 900 and the immediately adjacent structures. In oneimplementation, the separation caps 914 a, 914 b are porous endcaps(e.g., plates with pores or vents). In another implementation, theseparation caps 914 a and 914 b are valves that open under pressuregenerated by the input stream 908.

The getter element 900 includes a getter body (not shown) including agetter material that reacts with one or more volatile or non-volatilefission products 910, resulting in an output stream 912. The outputstream 912 exiting the getter element 900 has a lower volatile fissionproduct content level than the input stream 908 entering the getterelement 900. In one embodiment, the output stream 912 is vented from thefuel pin 920, such as through one or more pin vents of the fissionplenum 924.

In some implementations, the getter material reacts with one or morevolatile fission products 910 in the input stream 908 such as cesium,rubidium, strontium, etc. In additional or alternative implementations,the getter material of the getter body reacts with one or morenon-volatile fission products.

FIG. 10 illustrates a cross-sectional view of a fuel pin 1020 of anuclear reactor equipped with two example getter elements 1000 a, 1000 barranged in series between nuclear fuel 1022 and a fission plenum 1024.In operation, fission gas from the fuel 1022 is passed via an inputstream 1008 through the getter elements 1000 a, 1000 b in series. Withineach of the getter elements 1000 a, 1000 b, one or more fission products1010 within the input stream 1008 undergo chemical reactions with gettermaterial, thereby cleaning or partially cleaning the input stream 1008to reduce a concentration of the fission product 1010 in an outputstream 1012. Separation caps 1014 a, 1014 b, 1014 c are barriers thatare either porous or capable of selectively opening, such as underpressure of the input stream 1008.

In one implementation, the first getter element 1000 a includes a firstgetter material for targeting the uptake of a first fission product,while the second getter element 1000 b includes a second getter materialfor targeting the uptake of a second fission product. For example, thefirst material of the first getter element 1000 a may include a gettermaterial targeted for uptaking a first element or compound, while thesecond material of the second getter element 100 b may include a gettermaterial targeted for uptaking another compound including the firstelement and/or another different element. In one exemplaryimplementation, one of the two getter elements 1000 a and 1000 bincludes a getter material for uptake of cesium, such as niobium ortitanium oxides, while the other one of the two getter elements 1000 aand 1000 b includes a different getter material for uptake of iodine,such as silver, copper, or barium.

It is noted herein that fuel pin 1020 of FIG. 10 is not limited to twogetter elements or the materials listed above, which are provided merelyfor illustrative purposes. Other implementations may include fewer orgreater than two getter elements.

It is noted herein that the shape of the one or more getter elements(e.g., 1000 a, 1000 b) of the present disclosure is not limited to thecylindrical shape depicted in FIGS. 1-10. The one or more getterelements 1000 of the present disclosure may take on any generalgeometrical shape. In other implementations, the one or more getterelements take on a variety of shapes including without limitationhexagonal prism shapes, parallelepiped shapes, triangular prism shapes,helical shapes, conical shapes or the like. In one embodiment, the oneor more getter elements 1000 contained within the fuel pins 1020 arestructured so as to substantially conform to the internal shape of thefuel pins 1020. In this regard, the one or more getter elements 1000 maytake on any shape known in the art based on the shape of the fuel pins1020.

It is noted that the getter element(s) (e.g., 1000 a, 1000 b) of thepresent disclosure may be adapted to operate in any nuclear reactionenvironment. The nuclear fuel contained within the fuel pin 1020 mayinclude any fissile and/or fertile nuclear fuel known in the artincluding without limitation recycled nuclear fuel, unburned nuclearfuel, and enriched nuclear fuel.

In one embodiment, the fuel 1022 includes a metal nuclear fuel and isused to form a core of a metal fuel nuclear reactor along with aplurality of other fuel pins. In one embodiment, metal fuel nuclearreactor is a fast reactor. For example, the metal fuel nuclear reactormay include a breeder reactor, such as, but not limited to, a travelingwave reactor.

FIG. 11 illustrates a perspective view of a nuclear reactor core 1100including a set of fuel assemblies (e.g., a fuel assembly 1130). Eachfuel assembly further includes a set of fuel pins and each fuel pinincludes one or more getter elements, as discussed previously herein.

The structure and arrangement of the fuel assemblies of the reactor coremay take on any form known in the art. In the example arrangement ofFIG. 11, the fuel assemblies are arranged in a hexagonal array. It isnoted that the arrangement depicted in FIG. 11 is not a limitation onthe present disclosure and is provided merely for illustrative purposes.In some implementations, the fuel assemblies are arranged according toother shapes such as, but not limited to, a cylinder, a parallelepiped,a triangular prism, a conical structure, a helical structure and thelike.

FIG. 12 illustrates a top view of an example fuel assembly 1200including a set of fuel pins (e.g., a fuel pin 1120). Each of the fuelpins is equipped with one or more getter elements for cleaning a fissiongas to remove one or more volatile or non-volatile fission products. InFIG. 12, the fuel pins are cylindrically-shaped and are arranged in aclose packed hexagonal array; however, this arrangement may take onother forms in other implementations. For example, the fuel pins 1220 ofthe fuel assembly 1200 may individually be shaped hexagonally,parallelepiped, triangular, helical, conical or the like. In otherembodiments, although not shown, the fuel pins 1220 of the fuel assembly1200 may be arranged in a rectangular array, a square array, aconcentric ring array and the like.

FIG. 13 illustrates example operations 1300 for forming a getter bodyfor use in cleaning a fission gas output stream of a nuclear reactor. Adetermining operation 1302 determines an amount of fission productcontained within a fluid flow output from a nuclear fission reactor coreover a selected period of time. The selected period of time can be asingle or multiple fuel cycles and may be the expected lifetime of asingle fuel pin or fuel assembly of the reactor. It is to be appreciatedthat different fuel assemblies and/or fuel pins may have differentexpected lifetimes or fuel cycles which can be accommodated withdifferent expected fission product determinations for different fuelelements. The amount of fission product contained within the fluid flowfurther corresponds to a specific amount of nuclear fission fuelconsumed during the selected period of time which can be determinedusing any suitable neutronic methods and/or model of the present fueltype and expected neutronic environment of the fuel element (e.g., fuelburn up) over the specified period of time.

A providing operation 1304 provides a getter process mixture thatincludes a getter material reactive with a fission product of the fluidflow output from the nuclear fission reactor core. An amount of thegetter process mixture to use in forming the getter body is determinedby operations 1306 and 1308, described below.

Another determining operation 1306 determines a desired yield of areaction product to be formed via a chemical reaction between thefission product and the getter material over the selected period oftime. In one implementation, the desired yield of the reaction productis an amount calculated as resulting from a reaction between the gettermaterial and substantially all of the fission product determined in thedetermining operation 1302. Based on the desired yield of reactionproduct, another determining operation 1308 determines a volumeparameter of the getter process mixture that identifies an amount orvolume of the getter process mixture needed to yield the desired amountof reaction product in the selected period of time. The determiningoperation 1308 may also determine not only the amount of the getterprocess mixture but also a desired volumetric measure or density of thegetter material suitable for uptake of the volume parameter of thedesired yield of a reaction product. Specifically, the reaction product,when uptake occurs has a volume that may decrease the void structure orincrease the density of the getter material. By determining this volumeof the desired yield of the reaction product (or predetermined amount ofreaction product), a volumetric parameter of the getter material can beselected that matches or exceeds the determined volume of the desiredyield of the reaction product to ensure that fluid flow through thegetter material is maintained (which may be maintained at or above aselected flow rate or flow level) and/or volumetric swelling of thegetter material stays within design boundaries. For example, thevolumetric parameter of the getter material may include withoutlimitation, any one or more of pore size, pore concentration,theoretical density of the getter material, mass ratio of gettermaterial to sacrificial void forming structures, etc.

A forming operation 1310 forms a getter body defined by the determinedvolume parameter. The getter body is formed by the getter process. Insome implementations, the forming operation 1310 further entails placingthe getter body within a container (e.g., forming a final “getterelement” includes at least one channel or passageway for transmission ofgas or liquid therethrough).

In some implementations, the getter element includes a getter body inthe form of loose powder, a plurality of pellets, particulates, etc.,within a porous container. In other implementations, the getter body isformed by a number of chemical and/or physical processes that generate asolid (e.g., free-standing) structure, such as a solid structureincluding a number of interconnected pores or a plurality of voidregions. Thus, the getter element may not always include a container.The getter body may include channels or pores of a variety of othershapes, such as elongated channels. In still other implementations, thegetter body is formed by multiple different porous components (e.g., aplurality of free-standing porous pellets, porous diffusing components,etc.)

FIG. 14 illustrates a series of example operations 1400 for preparing agetter process mixture and forming a getter body with a plurality ofvoids (e.g., pores). The example operations 1400 disclose void creationvia use of sacrificial structures, which are structures that decompose(thereby forming ‘voids’ within the getter process mixture) upon thermaland/or chemical treatment. In other implementations (such as thosedescribed with respect to FIGS. 20-25 below), voids of the getter bodyare formed by other methodologies and/or other void-forming structures.For example, additive manufacturing, template replication, and directfoaming are all suitable methods for creating void-forming structuresthat do not utilize sacrificial void-forming structures.

A selecting operation 1402 selects volume of getter material to beincluded in the getter process mixture. The getter material may includeany single or combination of material known in the art suitable forchemically reacting with one or more volatile or non-volatile fissionproducts in a nuclear reactor. In one embodiment, the getter material isprovided in powder form. For example, the getter material provided instep 1402 includes, but is not limited to, a metal oxide powder. Forinstance, the metal oxide powder provided in step 1402 may include, butis not limited to, ZrO₂, TiO₂, MoO₂, MoO₃, NbO₂, Nb₂O₅, Ta₂O₅, VO₂,V₂O₅, and Cr₂O₃. Any of these and analogous materials have been shown toreadily react with one or more volatile fission products including, butnot limited to, Cs, CsBr, CsI, Rb, RbI, RbBr, or other Rb-compounds, Sror Sr-based compounds, and iodine (and its compounds). In addition toone or more reactive materials such those described above, the gettermaterial may also include one or more non-reactive components, such asbinders and structural stabilizers.

In one embodiment, the getter material includes a metal oxide powderwith a select particle size, such as an average particle size betweenabout 100 and 500 nm. In another embodiment, the getter materialincludes a metal oxide powder with an average particle size at or below100 nm. For example, the getter material may include, but is not limitedto, a volume of nanopowder having an average particle size below 100 nm.

A providing operation 1404 provides a volume of void-forming structures(e.g., sacrificial void-forming structures) for combination with thegetter material in the getter process mixture. In one embodiment, thevoid-forming structures include one or more organic materials known toundergo pyrolysis (e.g., chemical decomposition) at elevatedtemperature(s) in the absence of oxygen. For example, the organicmaterials may be selected so as to decompose at temperatures at or belowan applied sintering temperature (e.g., reached during heat applied in adensifying operation 1408, described below). The organic material usedto form the void-forming structures may be selected so as to breakdownat a temperature between 200 and 600° C. For instance, the void-formingstructures may be formed from an organic material that decomposes attemperature below approximately 500° C. (e.g., 330-410° C.). In oneembodiment, the sacrificial void-forming structures are formed from asynthetic organic material. For example, the void-forming structures maybe formed from any synthetic organic material known in the art, such as,but not limited to, polyethylene (PE), polymethylmethacrylate (PMMA),polyvinyl chloride (PVC), polystyrene (PS), nylon, naphthalene and thelike. In another embodiment, the void-forming structures are formed froma natural organic material. For example, the void-forming structures maybe formed from any natural organic material known in the art, such as,but not limited to, gelatine, cellulose, starch, wax and the like.

In still another embodiment, the void-forming structures break down uponchemical treatment. For example, the void-forming structures may beformed from one or more water soluble ionic compounds. In oneembodiment, the void-forming structures include one or more salts. Forinstance, the salt-based void-forming structures may include, but arenot limited to, NaCl, KCl, LiCl and the like.

In another embodiment, the void-forming structures include one or moremetal or ceramic compounds that react with one or more acidic leachingagents. Sacrificial templating using chemical treatment is discussedgenerally in H. Wang, I. Y. Sung, X. D. Li, and D. Kim, “Fabrication ofPorous SiC Ceramics with Special Morphologies by Sacrificing TemplateMethod,” J. Porous Mater., 11 [4] 265-71 (2004), which is incorporatedherein by reference in the entirety. Sacrificial templating usingchemical treatment is also discussed generally in H. Kim, C. da Rosa, M.Boaro, J. M. Vohs, and R. J. Gorte, “Fabrication of Highly PorousYttria-Stabilized Zirconia by Acid Leaching nickel from aNickel-Yttria-Stabilized Zirconia Cermet,” J. Am. Ceram. Soc., 85 [6]1473-6 (2002), which is incorporated herein by reference in theentirety. Sacrificial templating using chemical treatment is alsodiscussed generally in N. Miyagawa and N. Shinohara, “Fabrication ofPorous Alumina Ceramics with Uni-Directionally-Arranged Continuous PoresUsing a Magnetic Field,” J. Ceram. Soc. Jpn., 107 [7] 673-7 (1999),which is incorporated herein by reference in the entirety.

In one example sacrificial templating method, a solid template isimpregnated with a suspension including the getter material. Thestructure is solidified through one or more techniques known in the art(e.g., as explained in the above-referenced publications), and thetemplate structure is removed, such as by acidic leaching. For example,a coral may be impregnated with hot wax, the wax may be cooled, and thecoral can be leached out using a strong acidic solution.

In another embodiment, the void-forming structures include one or moresolids that undergo sublimation. For example, the sacrificialvoid-forming structures may include any solid that readily sublimes,such as, but not limited to, naphthalene. In this regard, the one ormore solid sacrificial void-forming structures may sublime out of thegetter process mixture to generate a porous structure.

The void-forming structures are capable of producing a void structurewith a volume sufficient to maintain a selected fission gas flow throughthe getter body. For example, the void-forming structures may createpores with a size distribution between 10 and 300 μm. The void-formingstructures may have, but are not limited to, an average size ofapproximately 100 micrometer, 150 micrometer, 50 micrometer, 30micrometer, etc., as appropriate for the determined void size. It isnoted herein that the size range listed above is not a limitation on thepresent disclosure and is provided merely for illustrative purposes. Theselected size and/or concentration of void-forming structures may dependon the desired size of voids of void-structure and the desired densityof the resultant getter body. Moreover, the size of the void-formingstructures may be selected so as to account for expected volumetricgrowth of the reactive material in the void structure.

The void-forming structures provided in the providing operation 1404 maytake on any shape known in the art, including without limitation thoseexample shapes illustrated in FIGS. 15A-15D of the present disclosure.

While much of the present disclosure focuses on solid void-formingstructures, this is not a limitation on the present disclosure. Rather,it is noted herein that void-structures may also be liquid or gas form.For example, the void-forming structures may include water and oils thatevaporate or sublimate out of the getter body to create void regions. Instill other implementations, the void-forming structures are gaseous inform, such as gases injected into a liquid structure including thegetter material (e.g., as in direct forming, a technique describedbelow).

A forming operation 1406 forms a getter process mixture that includesboth the volume of getter material and the volume of the void-formingstructures. For example, the getter material and void-forming structuresmay be mixed in any selected proportion to achieve a desiredvoid-structure in a resulting getter body. In one implementation, a massratio of getter material to void-forming structures may include, but isnot limited to, a ratio between 1:1 to 3:1. For example, the gettermaterial may be a nanopowder, and the mass ratio of the nanopowder tospherical PE void-forming structures may include, but is not limited to,one or more of the following: 1:1; 1:25:1; 1.5:1; 1.75:1; 2:1; 2.25:1;2.50:1; 2.75:1 or 3.0:1.

In one embodiment, forming operation 1406 mixes the getter material andthe void-forming structures via a wet mixing process. For example, thevoid-forming structures may be mixed with a solution to form a componentmixture solution which in some cases may be a suspension mixture (e.g.,including particles large enough to settle). Among other components, thesolution may include, for example, water or alcohol (e.g., ethanol).

The forming operation 1406 may, in some implementations, entail additionof a binder agent to the mixture including the void-forming structuresand getter material to aid in cohesion of the getter material and/or theforming of voids from the void-forming structures. The binder agent mayinclude any binder agent known in the art of powder processing. Forexample, the binder agent may include, but is not limited to,polyethylene glycol (PEG). For instance, the mixture of step 1406 mayinclude, but is not limited to, 1-10% binder agent by mass (e.g., 5% PEGby mass). Binder agents may be useful in both wet and dry mixingprocesses.

In one wet mixing process, a surfactant is added to a suspensionincluding the getter material, void-forming structures, and a solution.The surfactant serves to aid in the dispersion of the getter material(e.g., if in powder form). In one embodiment, the surfactant is added tothe solution prior to addition of the getter material and/or thesacrificial void-forming structures. The amount of surfactant added tothe suspension may include, but is not limited to, 0.05 to 2% by mass(e.g., 0.1% by mass). The surfactant may include any surfactant known inthe art such as, but not limited to, polyoxethlyene (20) sorbitanmonooleate.

In another example wet mixing process, the getter process mixture is asuspension (e.g., getter material, sacrificial void-forming structures,and solution) and is treated with an ultrasonic bath. For example, theultrasonic bath may be applied after addition of a binder agent and/orsurfactant (e.g., as described above). The ultrasonic bath may helpbreak up clumps of getter material powder and facilitate uniform mixingof the getter material and sacrificial void-forming structures in thesolution. Additional or alternative filtering of particulate matter maybe used including agitation, mesh filters, etc.

In any of the above-described embodiments including a suspension, theforming operation 1406 may further include one or more operations fordrying the suspension. For example, a furnace or oven may be used to drythe suspension.

In contrast to the above-described wet-mixing and drying techniques, theforming operation 1406 may also be a dry mixing process. For example, adry mixture including the getter material and the void-formingstructures may be mixed using any mixing device known in the art, suchas, but not limited to, a mixer, tumbler or the like. It is noted hereinthat a binder agent may also be employed in a dry mixing process. In onesuch implementation, a binding agent (e.g., PEG) is added to dry gettermaterial powder and the void-forming structures in a select proportion(e.g., 1-10% binder agent by mass).

A densification operation 1408 densifies the getter process mixture. Inone embodiment, the densification operations 1408 includes pressing thegetter process mixture at a selected pressure to form a consolidatedpellet. Although the applied pressure may vary from one implementationto another, the applied pressure is—in general—sufficient to form aself-supporting consolidated volume. In one implementation, thedensification operation 1408 applies a pressure in the range of 200 to1300 MPa (e.g., 750 MPa) to the getter process mixture.

The getter material and sacrificial void-forming structures may beconsolidated using any densification device and/or technique known inthe art. For example, the getter material and sacrificial void-formingstructures may be pressed into a pellet using any pellet die known inthe art of pellet processing. The density of the consolidated volume(e.g., the compressed getter process mixture) may be controlled by thedie pressure applied to the getter process mixture and/or by the amountof void-forming structure included in the getter process mixture.

In some implementations, the densification operation 1408 entailssintering. Sintering may, for example, include heating the getterprocess mixture to a selected temperature for a selected time. In oneimplementation, the getter process mixture is heated to a temperaturebetween about 1000 and 1500° C. and held at that temperature between 1and 24 hours. For example, the getter process mixture may be heated to atemperature of 1350° C. and held at that temperature for 4 hours. By wayof another example, the consolidate volume may be heated to atemperature of 1100° C. and held at that temperature for 8 hours. Thesintering of ceramic materials is generally discussed in Borg, R. J., &Dienes, G. J., An Introduction to Solid State Diffusion. San Diego:Academic Press Inc. (1988), which is incorporated herein by reference inthe entirety.

In some implementations, sintering of the getter process mixture cancause a thermal breakdown of the void-forming structures. Specifically,the void-forming structures may break down (e.g., undergo pyrolysis) andexit the getter body, leaving behind a solid getter body. In someimplementations, sintering is carried out in an atmosphere to enhancepyrolysis of the void-forming structures. For example, the sinteringstep may be carried out in the presence of an atmosphere containingoxygen (e.g., air).

In some implementations that utilize sintering, the densificationoperation 1408 further entails applying a pre-heat treatment to thegetter process mixture prior to sintering to help initiate and/or fullyfacilitate thermal breakdown of the void-forming structures. Forexample, the pre-heat treatment heats the getter process mixture to anintermediate temperature lower than a sintering temperature for a selectperiod of time so as to fully burn out the void-forming structures priorto sintering. For instance, the getter process mixture may be heated toan intermediate temperature between 400 and 800° C. and held at thatintermediate temperature for 1 to 10 hours. In one specificimplementation, the consolidated volume is heated to an intermediatetemperature of 500° C. for 4 hours.

In implementations that utilize heat treatment in the densificationoperation 1408, the temperature of the consolidated volume may becontrolled at a selected ramp rate. For example, a ramp rate is selectedfor use during the void-forming structure burn-off process to ensurethat the consolidated volume does not break apart prior to sintering. Inone implementation, the temperature of the consolidated volume is rampedat a rate between 0.1 and 5° C./min, such as, but not limited to, 1°C./min.

Notably, some implementations of the disclosed technology do not includethe densification operation 1408 (e.g., pressurization, heating,sintering.) For example, some void-forming structures may be capable offorming voids naturally, such as through settling. In still otherimplementations, the densification operation 1408 entails compactionwithout heating or sintering.

Various parameters of the densification operation 1408 may be selectableto control the density of the resulting getter element. For example, theratio of the amount (by mass) of getter material to void-formingstructures may be controlled so as to control the density of theconsolidated volume and, thus, the densified getter element. By way ofanother example, the pressure applied via the densification operation1408 may be controlled so as to control the density of the getterprocess mixture and the resulting getter element. Moreover, weights andsizes of the void-forming structures may be selected to form adistribution of voids describable by a particular size or shapegradient. For example, the distribution may form naturally via settlingor agitation of void-forming structures of different sizes or shapes. Inanother embodiment, multiple layers of void-forming structures withdifferent sizes and/or shapes are systematically created in the getterprocess mixture.

FIGS. 15A-15D illustrate example shapes of sacrificial void-formingstructures that decompose when subjected to thermal and/or chemicaltreatment. The sacrificial void-forming structures of FIGS. 15A-15D aremerely illustrative and non-limiting examples of structures that may beused to create “voids” in a getter body formed from a getter processmixture. Specifically, FIG. 15A illustrates an example volume ofsacrificial void-forming structures 1500 that are spherical in shape(e.g., a sacrificial void-forming structure 1502). In otherimplementations, the sacrificial void-forming structures are shapeddifferently, such as ellipsoids, oblate spheroids, prolate spheroids,etc. For example, FIG. 15B illustrates the quantity 1502 ofellipsoid-shaped sacrificial void-forming structures. FIG. 15Cillustrates an example volume 1504 of oblate-spheroid-shaped sacrificialvoid-forming structures, and FIG. 15D illustrates an example volume 1506of prolate-spheroid-shaped sacrificial void-forming structures.

It is noted herein that spheres formed from PE having a sizedistribution in the range of 50 and 200 μm display adequate thermaldecomposition at temperatures between 330 and 410° C. suitable for useas void-forming structures of the present disclosure.

FIG. 16 illustrates a conceptual view of a portion of a consolidatedvolume 1600 of a getter process mixture, such as that formed during thedensification operation 1408 described with respect to FIG. 14. Theconsolidated volume is a pressurized volume including a getter material1602 and void-forming structures 1604 that provide at least onethrough-channel 1606 that permits transport of a fluid flow through thevolume 1600.

FIG. 17 illustrates graph 1700 depicting the percentage of theoreticaldensity (TD) of a getter process mixture achieved as a function ofapplied die pressure. As shown in the graph 1700, density, as expressedin terms of percent of TD, increases with increasing die pressure. Inone implementation, density of a getter element is selected to balancefission product uptake in the getter element with the ability tomaintain sufficient flow through the getter element. In one embodiment,the density of the fabricated getter element is between 25 and 45% TD.For example, the density of the fabricated getter element may have adensity between 35 and 40% TD. In another implementation, the fabricatedgetter element has a density between 50-70% TD. In still anotherimplementation, the fabricated getter element has a density between 60and 70% TD.

FIG. 18A illustrates an example getter body 1800 including sacrificialvoid-forming structures 1806 intermixed with a getter material 1804.FIG. 18B illustrates the example getter body 1800 after undergoingthermal or chemical treatment that decomposes the sacrificialvoid-forming structures, leaving behind voids (e.g., a void 1808). Insome implementations, the getter body 1800 of FIG. 18B is subjected tohigh pressures and heat to transform the getter body 1800 into asintered pellet or other structure.

FIGS. 19A and 19B illustrate scanning electron microscopy (SEM) imagesof the void structure of a getter element formed using spherical PEvoid-forming structures, in accordance within one or more embodiments ofthe present disclosure. More specifically, FIG. 19A illustrates a radialcross-section of the fabricated getter element and depicts a number ofpores that form the overall void structure of the getter element. In oneembodiment, the average pore size of the illustrated void structure isbetween 50 and 200 μm. For example, the void structure may have, but isnot limited to, an average pore size of approximately 100-120 μm. It isto be appreciated that the void forming structures may have anyappropriate size and/or shape (or even various sizes and/or shapes) asmay be suitable. For example, the void forming structures may includestructures having a diameter greater than 200 μm.

FIG. 19B illustrates a zoomed-in view of a single pore of the voidstructure and depicts the grain structure of the sintered gettermaterial. It is noted herein that the getter element associated with theSEM images of FIGS. 19A and 19B may have a density within the rangesprovided above.

FIG. 20 illustrates a series of example additive fabrication operations2000 for forming a getter element. Unlike the getter body formingprocesses described above (e.g., operations 1400 described with respectto FIG. 14), the additive fabrication process operations 2000 form agetter body without using any sacrificial void-forming structures. Forexample, the additive fabrication operations 2000 may entail 3D printingto create voids, such as via a selective laser sintering process.

A providing operation 2002 provides a getter material. In oneembodiment, the getter material in provided in particulate form. Forexample, getter material may be a metal oxide powder (e.g., ZrO₂, TiO₂,MoO₂, MoO₃, NbO₂, Nb₂O₅, Ta₂O₅, VO₂, V₂O₅, and Cr₂O₃). In oneembodiment, the average particle size of the getter material is between100 and 500 nm. In another embodiment, the average particle is at orbelow 100 nm. It should be understood that a wide range of particlesizes, including those in excess of 500 nm, may be suitable for use indifferent implementations depending on the getter material andmanufacturing processes employed.

An additive formation operation 2004 uses an additive manufacturingoperation (e.g., 3D printing) to synthesize a free-standingthree-dimensional object from the getter material. Collectively, thefree-standing structures form a getter body (e.g., as shown and furtherdescribed with respect to FIGS. 22-24, below). One example suitableadditive manufacturing process is selective laser sintering. Selectivelaser sintering uses a laser to sinter powdered material by aiming andfiring the laser at points in space defined by a 3D model, therebybinding material together to create a solid structure. Selective lasersintering is generally described in U.S. Pat. No. 4,863,538, filed onOct. 17, 1986, which is incorporated above by reference in the entirety.

Elements manufactured via the example additive fabrication operations2000 may include any micro and/or macro-structure(s) capable ofmaintaining the fission product uptake for the given application, whichmay maintain sufficient flow through a getter element. A few examplegetter body structures are provided in FIGS. 21-23.

FIG. 21 illustrates an example getter body 2102 formed via an additivefabrication (e.g., 3D printing) process. Various elements (e.g., anelement 2104) of the getter body 2102 may assume different shapes andsizes in different implementation. In one implementation the elements ofthe getter body 2102 are not attached to one another, but rest freelywithin a container (e.g., a cylindrical container to create theillustrated distribution). In another implementation, the differentelements are interconnected. Spaces between the different elements ofthe getter body 2102 create transmission channels 2106 through whichfluid of an input stream 2108 may pass and come into contact with theactive surface of the transmission channels within the getter body 2102.

FIG. 22 illustrates another example getter body 2202 formed via anadditive fabrication (e.g., 3D printing) process. The getter body 2202is a single, free-standing structure including rows and columns of pores2206 to maximize surface area of contact between the getter body 2202and an input stream 2208.

FIG. 23 illustrates yet another example getter body 2302 formed via anadditive fabrication process. The getter body 2302 includes a number ofindividual elements (e.g., an element 2304) each added to aninterconnected structure via an additive fabrication process. Spacesbetween the different elements of the getter body 2302 createtransmission channels 2306 through which gas or liquid of an inputstream 2308 may pass and come into contact with surface area of thegetter body 2302.

The getter body 2302 includes different elements including differentgetter materials, as indicated by the shading in FIG. 23. For example, afirst element 2304 printed to a first portion of the getter elementincludes a first getter material, while a second element 2305 printed toa second portion of the getter element includes a second gettermaterial. In this regard, two or more types of materials may be providedin the single getter body 2302, facilitating a targeted uptake of two ormore types of fission products or more products from an input stream2308. For example, the first element 2304 may include a getter materialtargeted for uptaking cesium, while the second element 2305 includes agetter material targeted for uptaking another element or anothercompound of cesium. Other getter bodies formed by similar processes mayinclude greater than two getter elements for uptake of greater than twotarget fission products.

FIG. 24 illustrates example operations 2400 for forming a getter elementvia a sacrificial templating process. A providing operation 2402provides a suspension including a getter material reactive with atargeted fission product of a nuclear reaction. An impregnationoperation 2404 impregnates a porous template structure with thesuspension. A solidifying operation 2406 solidifies the suspension, anda removing operation 2408 removes the template structure, leaving behinda solidified getter element with a porous structure mimicking the poroustemplate. For example, the removal operation 2408 may entail a thermalor chemical treatment that causes the porous template structure todecompose.

FIG. 25 illustrates example operations 2500 for forming a getter elementvia a direct foaming operation. A providing operation 2502 provides asuspension including a getter material reactive with a target fissionproduct. An introduction operation 2504 introduces gas into thesuspension to form a foam that includes the getter material. A firstsolidifying operation 2506 solidifies the suspension, and a secondsolidifying operation 2508 solidifies the foam to form a solidifiedgetter element having a getter body that includes a void structurecreated by the gas.

The herein described components, operations, devices, objects, and thediscussion accompanying them are used as examples for the sake ofconceptual clarity and that various configuration modifications arecontemplated. Consequently, as used herein, the specific exemplars setforth and the accompanying discussion are intended to be representativeof their more general classes. In general, use of any specific exemplaris intended to be representative of its class, and the non-inclusion ofspecific components (e.g., operations), devices, and objects should notbe taken as limiting.

Furthermore, it should be understood that process operations describedherein may be performed in any order, adding and omitting as desired,unless explicitly claimed otherwise or a specific order is inherentlynecessitated by the claim language. The above specification, examples,and data provide a complete description of the structure and use ofexemplary embodiments of the disclosed technology. Since manyembodiments of the disclosed technology can be made without departingfrom the spirit and scope of the disclosed technology, the disclosedtechnology resides in the claims hereinafter appended. Furthermore,structural features of the different embodiments may be combined in yetanother embodiment without departing from the recited claims.

The invention claimed is:
 1. A getter element comprising: a getter bodyincluding a getter material reactive with a nuclear fission product, thegetter body further including a void structure through the gettermaterial forming at least one through-channel to facilitate a flow of aninput stream through the getter body, the void structure formed byremoval of a plurality of void forming structures that were mixed withthe getter material in the getter body.
 2. The getter element of claim1, wherein the at least one through-channel comprises a reaction surfacearea sufficient to accommodate a chemical reaction between substantiallyall of the fission product within the input stream over a predeterminedtime interval.
 3. The getter element of claim 1, wherein the at leastone through-channel includes a plurality of voids.
 4. The getter elementof claim 3, wherein the plurality of voids have a volume sufficient tomaintain a through-flow transmission above a selected flow level despiteexpansion of the getter material within a predetermined range ofexpansion.
 5. The getter element of claim 1, wherein the getter materialis formed of a metal oxide.
 6. The getter element of claim 5, whereinthe metal oxide includes one or more of zirconium oxide, titanium oxide,molybdenum oxide, niobium oxide, tantalum oxide, vanadium oxide, andchromium oxide.
 7. The getter element of claim 5, wherein the metaloxide has an average particle size between 100 nm and 500 nm.
 8. Thegetter element of claim 5, wherein the metal oxide has an averageparticle size of less than 100 nm.
 9. The getter element of claim 1,wherein the getter material is configured to react with a fissionproduct that comprises one or more of cesium and a cesium compound. 10.The getter element of claim 1, wherein the getter body has a densitybetween 25% and 45% of a theoretical density of the getter body.
 11. Thegetter element of claim 1, wherein the getter body has a density between50% and 70% of a theoretical density.
 12. The getter element of claim 1,wherein the getter body is formed of a first getter material tofacilitate a reaction with a first fission product in the flow of theinput stream and a second getter material to facilitate a secondreaction with a second fission product in the flow of the input stream.13. A getter element comprising: a getter body including a first gettermaterial reactive with a first nuclear fission product, the getter bodyincluding a second getter material reactive with a second nuclearfission product, the getter body further including a void structurethrough the first getter material and the second getter material thatforms at least one through-channel to facilitate a flow of an inputstream through the getter body, the at least one through-channelcomprising a plurality of substantially-spherical voids formed byremoval a plurality of void forming structures that were mixed with thefirst getter material in the getter body.
 14. The getter element ofclaim 13, wherein the at least one through-channel comprises a reactionsurface area sufficient to accommodate a chemical reaction betweensubstantially all of one or more of the first fission product and thesecond fission product within the input stream over a predetermined timeinterval.
 15. The getter element of claim 13, wherein the plurality ofvoids have a volume sufficient to maintain a through-flow transmissionabove a selected flow level despite expansion of the first gettermaterial and the second getter material within a predetermined range ofexpansion.
 16. The getter element of claim 13, wherein one or more ofthe first getter material and the second getter material are formed of ametal oxide.